1. Field of the Invention
The present invention relates to gear shift systems for transmissions in which a reverse gear shift stage is established by moving a reverse idle gear from a neutral position to a reverse position by means of a reverse shift fork.
2. Description of the Prior Art
FIG. 14 shows a gear shift system for a manual transmission of the prior art. A reverse shift fork 02 whose middle part is pivotally supported by a fulcrum pin 01, has an L-shaped long hole 02a at one end and a U-shaped fork channel 02b at the other end. A drive pin 03 fixed on a shift piece (not illustrated), engages with the long hole 02a, and a reverse idle gear 04 which can move freely in the axial direction engages with the fork channel 02b. 
When the shift piece is in a neutral position, the drive pin 03 provided on the shift piece is positioned at the bend in the middle of the L-shaped long hole 02a of the reverse shift fork 02 (broken line). When the drive pin 03 moves from this state towards a reverse position, which is upwards in the figure, the reverse shift fork 02 whose long hole 02a is pushed by the drive pin 03, moves clockwise in a circular manner, and its fork channel 02b moves the reverse idle gear 04 downwards (as shown in the figure) to establish a reverse gear shift stage (solid line). On the other hand, when the drive pin 03 moves from the reverse position to the neutral position, the reverse shift fork 02 whose long hole 02a is pushed by the drive pin 03, moves anticlockwise in a circular manner, and its fork channel 02b moves the reverse idle gear 04 upwards (as shown in the figure) to release the established reverse gear shift stage. When the drive pin 03 moves from the neutral position towards a fifth speed position which is on the opposite side to the reverse position, the drive pin 03 slips inside the long hole 02a, the reverse shift fork 02 remains stopped at the position shown by the broken line, and the reverse idle gear 04 is maintained in the neutral position.
In the above-described prior art device, since the drive pin 03 provided on the shift piece engages with the long hole 02a provided on the reverse shift fork 02 and the reverse shift fork 02 moves in a circular manner between the neutral position and the reverse position through movement of the drive pin 03, there is the problem that galling or non-smooth sliding is caused between the drive pin 03 and the long hole 02a, preventing smooth operation and thus degrading the shift feeling when establishing and releasing the reverse shift state.
The present invention has been carried out in view of the above-mentioned circumstances and it is an objective of the present invention to improve the shift feeling by carrying out smooth transfer of an operational load between a shift rod and a reverse shift fork.
In order to achieve the above-mentioned objective, a transmission gear shift system is provided which comprises a reverse shift fork supported on a transmission case in a circularly movable manner via a fulcrum pin and a shift rod for driving the reverse shift fork supported on the transmission case in an axially movable manner. The reverse shift fork is moved in a circular manner in one direction by movement of the shift rod from a neutral position to a reverse position and a reverse idle gear is shifted from a neutral position to a reverse position by the reverse shift fork to establish a reverse gear shift stage. The reverse shift fork is moved in a circular manner in the other direction by movement of the shift rod from the reverse position to the neutral position and the reverse idle gear is shifted from the reverse position to the neutral position by the reverse shift fork to release the established reverse gear shift stage. A drive cam face for reverse shift and a drive cam face for neutral return are provided on a drive cam which is integral with the shift rod. A driven cam face for reverse shift and a driven cam face for neutral return are provided on the reverse shift fork, and the movement of the shift rod from the neutral position to the reverse position presses the drive cam face for the reverse shift of the drive cam against the driven cam face for reverse shift of the reverse shift fork to move the reverse shift fork in a circular manner in the one direction, and the movement of the shift rod from the reverse position to the neutral position presses the drive cam face for neutral return of the drive cam against the driven cam face for the neutral return of the reverse shift fork to move the reverse shift fork in a circular manner in the other direction.
In accordance with the above-mentioned arrangement, since movement of the shift rod from the neutral position to the reverse position presses the drive cam face for reverse shift of the drive cam against the driven cam face for reverse shift of the reverse shift fork to move the reverse shift fork in a circular manner to the reverse position, and movement of the shift rod from the reverse position to the neutral position presses the drive cam face for neutral return of the drive cam against the driven cam face for neutral return of the reverse shift fork to move the reverse shift fork in a circular manner to the neutral position, the shift fork can be operated smoothly by the drive cam without causing galling, and thus the shift feeling when establishing and releasing a reverse gear shift stage, can be improved.
In accordance with the invention, a transmission gear shift system is proposed wherein a driven cam face for neutral hold which extends from the driven cam face for neutral return is provided on the reverse shift fork, and when the shift rod moves from the neutral position to a forward position which is in the opposite direction to the reverse position in order to establish a forward gear shift stage, the drive cam face for neutral return of the drive cam, moves along the driven cam face for neutral hold of the reverse shift fork, while maintaining the reverse shift fork in the neutral position.
In accordance with the above-mentioned arrangement, since the driven cam face for neutral hold which extends from the driven cam face for neutral return is provided on the reverse shift fork, when the shift rod moves from the neutral position to a forward position which is in the opposite direction to the reverse position, in order to establish a forward gear shift stage, the drive cam face for neutral return moves along the driven cam face for neutral hold while maintaining the reverse shift fork in the neutral position, and it is possible to prevent unnecessary circular movement of the reverse shift fork from the neutral position accompanying the movement of the shift rod to the forward position.
In accordance with the invention, a transmission gear shift system is proposed wherein movement of the reverse idle gear in the direction away from an end face of the transmission case is restricted by the drive cam face for neutral return of the drive cam causing the reverse idle gear to be pushed against the end face when in neutral.
In-accordance with the above-mentioned arrangement, since movement of the reverse idle gear in the direction away from the end face of the transmission case is prevented by the drive cam face for neutral return of the drive cam causing the reverse idle gear to be pushed against the end face when in neutral, it is possible to effectively maintain the reverse idle gear in the neutral position without providing a special detent mechanism on the reverse shift fork, and thus this can contribute to a reduction in the number of parts.
Further, in accordance with the invention, a transmission gear shift system is provided wherein movement of the reverse idle gear in the direction away from an end face of the transmission case is restricted by the drive cam face for reverse shift of the drive cam, causing the reverse idle gear to be pushed against the end face when a reverse gear shift stage is established.
In accordance with the above-mentioned arrangement, since movement of the reverse idle gear in the direction away from the end face of the transmission case, is prevented by the drive cam face for reverse shift of the drive cam, causing the reverse idle gear to be pushed against the end face when a reverse shift gear stage is established, it is possible to effectively maintain the reverse idle gear in the reverse position without providing a special detent mechanism on the reverse shift fork and thus this can contribute to a reduction in the number of parts.